Degree day

Degree days (even degree day, GTZ, Gt) and heating degree day (HDD, G) are used to calculate the heating requirements of a building during the heating season. They represent the correlation between room temperature and the outside air temperature for the heating days the measurement period and are thus a means to determine the heating and Heizstoffbedarfs.

Degree days and heating degree days are specified using the unit Kelvin (K or ° C), so they have the same dimension as the temperature ( or heat sum in Kd or ° Cd, degree days ). However, they are also related to a heating season or a calendar month and then are meaningful to the seasonal variations. There is one value for the long-term climatic means, and a value for the current weather ( meteorological measurement).

2.1 Comparison of degree days and heating degree day
2.2 degree days for a month

3.1 Budgeting
3.2 Cost Accounting
3.3 Climatology

Definition

Reference values of ambient temperature and heating limit

Reference values are the room temperature and the heating limit. For the reference values , there are different uses:

After the German VDI guideline 2067/DIN 4108 T6, the internal temperature at 20 ° C and the heating limit is assumed at 15 ° C is added to GTZ20/15. For the outside temperature one assumes the determined by the DWD, respectively MeteoAM values;
In Austria, Switzerland and Liechtenstein to using an internal temperature of 20 ° C and a heating limit of 12 ° C is added to HGT20/12. Here are the temperature values of ZAMG ( Austria ) and MeteoSwiss ( Switzerland and Liechtenstein ) reference value.

Degree days according to VDI 2067 / heating degree day ÖNORM B 8135 and SN 565381-3

The number of degree days or GTZ Gt is calculated when the outdoor temperature is below the heating limit. It is the sum of the differences between an assumed room indoor temperature of 20 ° C and the respective daily average outdoor temperature all days of a period in which it is below the heating limit temperature of the building.

It is a position-dependent parameter which reflect local climatic conditions. It is a GTZnorm for the long-term average, and a distinguished GTZspez for the current measurement. The latter is used for example for the cleanup of air consumption readings.

According to VDI 2067 Central heating: Calculating the cost of heat supply systems:

With

The number of degree days one day ( heating degree day value ) is the difference between the inside air temperature and the daily mean value of the outdoor temperature.
The number of degree days for the heating time is the sum of the differences between the average room temperature of 20 ° C and the daily averages of air temperature of all heating days in the standard local heating season (September 1 to May 31 ).
During the heating period only the degree days heating days are considered to be within the heating period.
The degree days of the month is the sum of the temperature differences over the month.

The method, as the VDI 3807 indicating with distinction of degree days and heating degree day GTZ G, is in the Austrian ÖNORM B 8135 Simplified calculation of time-related heat loss ( heat load ) of buildings or of the Swiss SIA 381-3; SN 565381-3:1982 heating degree days in Switzerland not performed, it is also the term heating degree day degree days for HGT to VDI.

Heating days and heating degree days, in addition to climatic region, altitude and standard outside temperature (which is the usual local median minimum temperature, ie, the characteristic size of the full load) performed in the Austrian energy certificate.

Since affect besides the air temperature nor wind, humidity and solar radiation on the energy required for heating, the number of degree days / HGT is suitable only for rough estimation. About a correction of the standard room temperature with respect to the real measured inside temperature is Heizziel and residential location specific situations can be taken into account.

Heating degree days according to VDI 3807

Are very similar to the heating degree days (G ) according to VDI 3807 Blatt 1 determines energy consumption characteristics for buildings, but it is the actual building specific heating temperature limit used.

It reflects the heat load of a concrete building, and takes into account the thermal insulation of the building, heat flows from sources other than the heater. Because in the individualized heating limit also enters the desired internal temperature, the housing situation is considered. In addition, one also distinguishes an average value GHGm, and a value of the current heating season, GHG, and shall take into account the progress of the outside temperature during the observation period, which may differ from long-term average.

With

The heating degree days according to VDI 3807 are in good energy standard slightly below the number of degree days VDI 2067/einfachen heating degree days HGT.

Examples of calculations

Comparison of degree days and heating degree day

Both VDI values can be converted into each other, for example, corresponds GTZ15/15 G15. The following table gives a ( day ) Example values represent:

Degree days for a month

It is believed that the heating temperature limit is 15 degrees and the interior temperature should be 20 degrees. The heating limit temperature and the internal temperature can be varied. For individual days ( eg, April 29 ) must not be charged any degree day, since the day was warmer than the heating temperature limit of 15 degrees on average.

For the calculation of the number of degrees temperature, therefore, the average temperature per day is needed at one site.

Application

Degree days are always used in the Heizbedarfsrechnung and heating bill, if no measured values are available or the billable period measured is different. In this case, however, not the absolute values for the application, but come thousandth ( parts per thousand ) relative to a year. According to VDI 2067 or DIN 4713 which are on average:

Budgeting

The number of degree days is used to estimate the heating energy demand of a building in a particular location and also serves for normalization ( weather adjustment ) of heating energy consumption.

Dividing the heating degree-days of heating period by the number of heating days or the annual value by 365 (average day Heizgrade ), we obtain an estimate of the sizing of the heating system, we can calculate the number of degrees for the minimum temperature, a characteristic value of the required full load.

The heating degree days for G12 Basel ( favored atlantic, Köppen Cfb ) are 3000 (Medium 1991-2000 ), medium Heizgrade 8.2; the average low temperature is about -2 ° C, which is the necessary medium full load is about 10 heating degree days, 25 Heizgrade ( temperatures below -13 ° C) are exception events;
Heating degree days for G12 Neusiedl in Burgenland ( Pannonian, Köppen Dfb) amount to 3102 (average 1971-2000 ), the middle Heizgrade 8.5; the average January low temperature so is -3.0 ° C, the mean maximum -day Heizgrade at 15, the standard outside temperature ( tabulated average minimum temperature ) at -12 ° C ( 24 heating degree days ), the measured minimum temperature was in the three decades -20.5 ° C, the hypothetical maximum Heizgrade ie 32.5;
Heating degree days for G12 Tamsweg in the Salzburg Lungau ( intra- alpine basin, Köppen Dwc, one of the cold poles of Austria) amount to 4657, average Heizgrade 12.75, mean maximum Heizgrade 22.3 (mean cold January -10.3 ° C), standard outside temperature -22 ° C (34 degree of heating ), and maximum Heizgrade 40.3 ( -28.3 ° C).

Heating demand is given by ( ÖNORM B 8135 ):

Using the following formula, a specific heating energy consumption () climate adjusted are specified as:

Which indicates the long-term average for the period under consideration.

So you can see if changing consumption climatic causes ( severe winter ) or come from changing heating behavior of users.

Cost accounting

Where the total heating costs for example 625 euros per calendar year, which accounts for 200 euros on the first two months of the year. (625 € x (170 150 ) / 1000 = 200 EUR )

If it is a leap year, is the daily value in February not more 150/28 = 5,357, but according to 150/29 = 5.172. However, this only plays a role if the period reckoned begins or ends, as the monthly values are not adjusted for leap year in February.

Climatology

Increasingly, the Heizgradrechnung is also used in climatology because it precise statements on climate change than meets about mean temperatures. So sank in Basel (one of Europe's longest time series has, is climatically favorable on the Rhine ) the Gradtagzahen (20 /12) in the half- century from 1961 to 2011 steadily from about 3400 to about 2800, which is a decrease of about 15 percent (3400 is about the current average of Bern and Zurich in the Central Plateau ). The annual extreme events declined even almost by half ( maximum year in the interval 1963 through 3800, minimum 2007: below 2300 - the former corresponds to the present value of St. Gallen at the edge of the Alps, the latter more about Lugano, on the southern side ).

The data can also be for a - anthropocentric - used " living " climate classification, so the EU project Keep Cool II has created an EU Klimazonierung in which the heating degree days were divided by the cooling degree days in the frame.

Deutscher Wetterdienst Oceanic climate Growing degree-day

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